1. Technical Field
The present invention relates to an articulated hauler or truck, such as a dumper. The truck includes a vehicle part having a drive engine and a load-bearing vehicle part. The vehicle parts are interconnected in an articulated manner about a vertical pin. The load-bearing vehicle part is provided with at least one wheel axle driven by the drive engine via a mechanical transmission and arranged at a distance from the vertical pin. The vehicle part with the drive engine is provided with at least one wheel axle driven by the drive engine and arranged at a considerably shorter distance from the vertical pin.
2. Background Information
It is previously known to provide an articulated truck such as a dumper with all-wheel drive in order to obtain good passability when driving on soft and/or slippery surfaces. To accomplish this, the drive line of the truck includes a front wheel axle arranged in a front vehicle part with a differential that, via a propeller shaft, is driven, via a distribution gearbox, by a gearbox arranged in the drive engine of the truck. The distribution gearbox also transmits the torque of the drive engine to a rear wheel axle differential arranged in a rear vehicle part via a second propeller shaft. In the event that the truck is provided with a second rear wheel axle, the torque of the drive engine is transmitted between the first rear wheel axle and the differential of the second rear wheel axle via a further propeller shaft arranged between the wheel axles. The differentials make it possible for the wheels on one and the same axle to cover distances of different length that may occur, such as when cornering and negotiating obstacles. As long as the wheels have a good grip, this works well. However, if the grip of one of the wheels on a wheel axle worsens, the wheel starts to slip, and the power of the drive engine is consequently led out to the slipping wheel. Accordingly, the grip of the slipping wheel decides the combined driving power of the two wheels. Against this background, a differential lock is usually arranged so as to lock the differential, making the wheels rotate at the same speed.
As known in the art, a longitudinal differential is also arranged between the front wheel axle of the front vehicle part and the rear wheel axle of the rear vehicle part in a manner corresponding to the differentials described above. This is done in order to make it possible for the wheels on the front and rear wheel axles to cover distances of different length, for example, when cornering or negotiating obstacles. As long as all wheels have a good grip, this works well. However, if the grip of the wheels on one wheel axle becomes worse (usually the front wheel axle in the case of a loaded vehicle), the wheels start to slip, and the power of the drive engine is then led out to the slipping wheel(s). The longitudinal differential is therefore also provided with a differential lock arranged so as to lock the differential, causing all the wheels to rotate at the same speed.
The above-mentioned differential locks are operated by the driver of the truck, who is therefore responsible for both engaging and disengaging the locks. As trucks of the above-mentioned type are often used on sites with very varied surfaces, for example, alternately mud and asphalt, frequent engagement and disengagement of the differential locks is required in order to avoid increased wear/stress on the transmission of the truck.
A particularly marked problem occurs in articulated trucks such as a dumper having a front vehicle part pivotally connected about a vertical pin to a rear vehicle part, where the rear vehicle part has a wheel axle arranged at a distance from the vertical pin, and the front vehicle part has a front wheel axle arranged at a considerably shorter distance from the vertical pin. During cornering, the wheels on the wheel axles run on considerably different turning radii. If the truck is driven through a curve with the longitudinal differential lock engaged, particularly when loaded and/or on a surface with good grip, the transmission is subjected to great restrained torques due the wheels on the front wheel axle trying to rotate at a higher speed than the wheels on the rear wheel axle. In addition to the stresses on the transmission, this also results in increased tire wear and an impaired driving feeling when the truck is under-steered, that is to say, tries to go straight on during cornering.
The present invention provides a solution to the above-mentioned problems by producing an articulated truck in which great restrained torques in the transmission of the truck associated with cornering, are avoided. This is achieved by providing an articulated lorry, such as a dumper, having a vehicle part containing the drive engine and a load-bearing vehicle part. The vehicle parts are pivotably interconnected about a vertical pin. The load-bearing vehicle part is provided with at least one first wheel axle driven by the drive engine via a mechanical transmission, with the axle being arranged at a distance from the vertical pin. The vehicle part bearing the drive engine is provided with at least one second wheel axle driven by the drive engine. This second wheel axle is arranged at a considerably shorter distance from the vertical pin than the first wheel axle. The second wheel axle is also driven via a hydrostatic transmission. As the first wheel axle on the load-bearing vehicle part is driven by the drive engine via a mechanical transmission, the driving torque of the drive engine is transmitted to those wheels which, when the vehicle is loaded, can be expected to have the best grip. At the same time, part of the driving torque of the drive engine can be transmitted to the second wheel axle, even during cornering, without great restrained torques arising.
According to a preferred embodiment of the invention, the hydrostatic transmission comprises a hydraulic pump driven by the drive engine and coupled to a hydraulic motor. The hydraulic motor is arranged for driving the second wheel axle, and is arranged at the differential of the second wheel axle. By arranging the hydraulic motor at the differential of the wheel axle, only one hydraulic motor is required for driving both wheels of the wheel axle, contributing to both weight-saving and simplified installation as relatively little space is required.
According to another preferred embodiment of the invention, the hydraulic pump is coupled to other hydraulic components arranged on the truck. This results in both weight-saving and simplified installation by virtue of the fact that fewer hydraulic pumps have to be accommodated in the space which is available in connection with the drive engine of the lorry.
According to another preferred embodiment of the invention, the hydraulic pump is coupled to tipping cylinders arranged for tipping a container arranged on the load-bearing vehicle part. This enables all of the oil flow delivered by the hydraulic pump to be used for propulsion when the truck is driven. When the truck is stationary, in connection with tipping, all of the oil flow is then available for the tipping cylinders.
According to another preferred embodiment of the invention, a coupling is arranged between the hydraulic motor and the second wheel axle for selective coupling of the hydraulic motor to the second wheel axle. This allows the driving wheels on the hydrostatically driven second wheel axle to be uncoupled, for example, when driving on roads, resulting in reduced transmission losses and, accordingly, reduced fuel consumption.
According to another preferred embodiment of the invention, the coupling is a toothed coupling that is preferably pneumatically operated between a coupled position and an uncoupled position. In this way, a robust coupling is obtained which can be engaged and disengaged during truck trips without being damaged.
According to another preferred embodiment of the invention, a detector is arranged so as to detect a driving situation in which the coupling is adapted so as to uncouple the hydraulic motor from the second wheel axle. By automating the engagement and disengagement of the drive to the second wheel axle based on the current driving situation, unnecessary driving with the drive engaged is avoided, resulting in reduced fuel consumption and reduced wear on the hydrostatic transmission. In this context, the detector is connected to an electronic control unit which engages or disengages the drive on the second wheel axle depending on the detected driving situation.
According to another preferred embodiment of the invention involving a driving situation concerning the speed of the tuck, the hydraulic motor is arranged so as to be uncoupled from the second wheel axle when a predetermined speed is exceeded. Another driving situation involves the current gear used in the gearbox of the truck. The above driving situations can be used as indicators that the truck is being driven under conditions wherein the drive of the second wheel axle is not required.
Further preferred embodiments and advantages of the invention can be understood by the following description.